1. Field of the Invention
The present invention relates to a resonant converter.
2. Description of the Related Art
A converter is a device for converting a DC voltage into at least one DC voltage. In some cases the DC output voltage is greater, in others less than an input voltage. The converter is mainly used for battery power supplies such as power electronic devices, particularly mobile phones and laptop computers.
A resonant converter is widely used because it can improve power conversion efficiency.
In general, a resonant converter includes a transformer, and maintains the DC output voltage that is output through an output terminal coupled to a secondary coil of the transformer by controlling an on/off drive frequency of two switches Q1 and Q2 coupled to a primary coil of the transformer receiving the DC voltage. For this, the resonant converter includes a feedback loop for transmitting a voltage or a current of an output unit to the primary coil of the transformer through an element such as an opto coupler or a shunt regulator.
A general resonant converter performs a protection function for preventing circuit elements from being damaged by controlling power transmitted to an output load side by controlling switching frequencies of the two switches Q1 and Q2 of the primary coil of the transformer under an abnormal operation condition such as an overload or an output terminal short. The power input to the resonant converter can be sequentially varied within a short period in which the two switches Q1 and Q2 are turned on/off once. In order to check whether an overload or an output terminal short is generated corresponding to the change of the input power, the general resonant converter can include a low pass filter for acquiring an average of input power within the period of operation.
However, in some general resonant converters it is difficult to quickly control the input power because of a delay time of the low pass filter when high power is instantly input at the input terminal, and hence, drive stability for the resonant converter is not optimal.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.